try to harden seqRecord against race condition

src/rec/seqRecord.c

@@ -174,6 +174,7 @@ static long process(seqRecord *prec)
   linkDesc	*plink;
   unsigned short	lmask;
   int			tmp;
+  int			index;
 
   if(seqRecDebug > 10)
     printf("seqRecord: process(%s) pact = %d\n", prec->name, prec->pact);
@@ -230,6 +231,7 @@ static long process(seqRecord *prec)
   }
   /* Figure out which links are going to be processed */
   pcb->index = 0;
+  index = 0;
   plink = (linkDesc *)(&(prec->dly1));
   tmp = 1;
   while (lmask)
@@ -241,23 +243,21 @@ static long process(seqRecord *prec)
     if ((lmask & 1) && ((plink->lnk.type != CONSTANT)||(plink->dol.type != CONSTANT)))
     {
       if (seqRecDebug > 4)
-	printf("  seqRec-process Adding link %d at index %d\n", tmp, pcb->index);
+        printf("  seqRec-process Adding link %d at index %d\n", tmp, index);
 
-      pcb->plinks[pcb->index] = plink;
-      pcb->index++;
+      pcb->plinks[index++] = plink;
     }
     lmask >>= 1;
     plink++;
     tmp++;
   }
-  pcb->plinks[pcb->index] = NULL;	/* mark the bottom of the list */
+  pcb->plinks[index] = NULL;	/* mark the bottom of the list */
 
-  if (!pcb->index)
+  if (!index)
   { /* There was nothing to do, finish record processing here */
     return(asyncFinish(prec));
   }
 
-  pcb->index = 0;
   /* Start doing the first forward link (We have at least one for sure) */
   processNextLink(prec);
 
@@ -367,6 +367,14 @@ static void processCallback(CALLBACK *arg)
   if (seqRecDebug > 5)
     printf("processCallback(%s) processing field index %d\n", prec->name, pcb->index+1);
 
+  if (pcb->plinks[pcb->index] == NULL)
+  {
+    static int overrun = 0;
+    errlogPrintf("seq record %s: index overrun number %d in callback.\n", prec->name, ++overrun);
+    dbScanUnlock((struct dbCommon *)prec);
+    return;
+  }
+
   /* Save the old value */
   myDouble = pcb->plinks[pcb->index]->dov;